1. Field
The subject invention relates to power delivery and in particular to systems and methods for providing a diverse source of power to a critical load in a power subsystem.
2. Related Art
Power distribution systems are typically used in facilities to convert transmitted high voltage energy to energy that is suitable for its intended use and deliver that energy within the facility. These facilities (e.g., hospitals, data centers, etc.) have a load (e.g., computers, heating and air conditioning equipment, etc.) to which the energy is delivered by the power distribution system. An exemplary power distribution system that is used in these facilities is a distributed redundant power system.
In a distributed redundant power distribution system, N+1 redundancy is achieved by providing two sources of power to a single load (e.g., servers and other IT equipment, chillers, etc.) from two diverse, totally independent sources. When there are only two such sources, there is only one combination (A+B). The system, therefore, has 2 N redundancy. When the system has three sources (A, B and C), there are three combinations of two: A and B, B and C and A and C. Similarly, when there are four sources (A, B, C, and D), there are six combinations of two: A and B, B and C, A and C, A and D, B and D an C and D. When there are five systems, there are ten combinations; and, when there are six systems, there are fifteen combinations.
Loading of the system using multiple sources can be as high as (1−1/N) times the total system capacity without overloading any system in the event of a single source failure. The criteria for achieving this maximum limit are that every possible combination of two systems needs to provide two-source power to an equal amount of load. For example, for five sources, there are ten load blocks, each of which needs to supply two source loads of 10% of the total load served. The total load can then be as high as 80% of the total system capacity.
For five 675 KW sources, for example, the total capacity is 3375 KW which would yield 2700 KW of distributed N+1 capacity as long as each of the ten combinations of two sources is loaded to 270 KW, split between the two sources such that when one source fails the load on the other source increases to no more than the sum of the load on both sources when both are energized. This configuration and loading would put a normal load of 540 KW on each source. Failure of any source causes the paired source in each of the four two-source combinations with that failed unit to assume half the 270 KW supplied by the two-source combination. This load assumption raises each of the four remaining sources from 540 KW to their maximum capacity of 675 KW.
The above system provides N+1 redundancy at all times that the five diverse sources are available. Maintenance activities, either planned or corrective, normally affect only a single source. However, any such maintenance results in the sources conceivably operating at 100% load. A single failure in the system while one source is out of service overloads all the other sources which can cause cascading service outages that could escalate to an entire system outage.